344 SCIEXCE PROGRESS. 



Somewhere in the neighbourhood of these reserve ma- 

 terials therefore, sometimes in the very cells containing the 

 reserves, the enzyme may be expected to occur. Where 

 not in the cells themselves, it might well be supposed that 

 the differentiation of internal tissues would lead to the local- 

 isation in special cells of the agent needed for digestion. 



In attempting to identify the localities, two methods of 

 procedure are open to the inquirer. The microscope will 

 show their presence, if they are sufficiently distinctive to 

 present any peculiar structure or reactions. Or their 

 presence may be ascertained by putting pieces of tissue 

 which are suspected to contain them, in such conditions as 

 will lead to their action, and the formation of recognisable 

 products. 



Both these methods present considerable difficulty, but 

 both have been attempted, and with more or less success. 

 In the case of animal cells, which are most easy to examine 

 by the methods familiar to the histologist, the protoplasm 

 of secreting gland cells has been found to show a peculiar 

 and characteristic granularity, and the amount of the granules 

 has been found to vary pari passu with the amount of 

 ferment that can be extracted from them. When applied 

 to vegetable histology, however, the granularity fails to be 

 a guide on which reliance can be absolutely placed. The 

 vegetable cell usually contains relatively little protoplasm, 

 and the materials found to be in solution in the cell-sap 

 interfere very much with the processes of staining. 



It has, however, been shown, though in somewhat 

 general fashion, that where a vegetable tissue is the seat 

 of an active zymotic power, the cells are found to possess 

 a markedly granular protoplasm. Gardiner (3) pointed this 

 out in the cells of Dionaea, the Venus's fly-trap, where the 

 glands are comparatively isolated in position. Brown and 

 Morris (4) showed it to be the case in the epithelium of a 

 particular part of the seed of the grasses, from which they 

 extracted two different enzymes. Marshall Ward (5) found 

 coarse granularity in certain fungi, when ferment could be 

 proved to exist in the same hyphae as the granules ; other 

 observers have found the same appearances in pollen tubes 



